1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device and a method of fabricating an LCD device, and more particularly, to a trans-reflection type LCD device and a method of fabricating a trans-reflection type LCD device.
2. Discussion of the Related Art
As demand for various types of display devices increases, efforts have been made to develop various flat display devices, such as liquid crystal display (LCD) devices, plasma display panel (PDP) devices, electroluminescent display (ELD) devices, and vacuum fluorescent display (VFD) devices. Currently, some type of the flat display devices have been incorporated into various display equipment.
Among the various types of flat display devices, the LCD devices have been commonly used in portable devices due to their advantageous characteristics, such as thin profile, light weight, and low power consumption. Thus, the LCD devices are commonly substituted for cathode ray tube (CRT) display devices. In addition, the LCD devices have been developed for computer monitors and television systems to receive and display broadcast signals.
The LCD devices are usually driven by making use of optical anisotropy and polarizing characteristics of liquid crystal molecules of liquid crystal materials. The liquid crystal molecules have long and thin structures, whereby it is possible to align the liquid crystal molecules along a specific direction. For example, when an electric field is induced to the liquid crystal material, the liquid crystal molecules become aligned along the specific direction. Thus, by controlling the alignment direction of the liquid crystal molecules, light is refracted according to the alignment direction of the liquid crystal molecules, thereby displaying an image.
The LCD devices are classified into one of reflective-type LCD devices and transmitting-type LCD devices. In the transmitting-type LCD devices, light is emitted from a backlight and transmitted to an LCD panel, thereby displaying an image. However, in the reflective-type LCD devices, ambient or front light is reflected within a reflecting plate of an LCD panel to display an image.
In general, a transreflection-type LCD device selectively uses both a transmission and reflection method to display an image. For example, the transreflection-type LCD device uses light emitted from a backlight, and ambient light or a light source, thereby decreasing power consumption.
FIG. 1 is a perspective view of a transreflection-type LCD device according to the related art. In FIG. 1, a transreflection-type LCD device includes upper and lower substrates 10 and 20 facing each other, and a liquid crystal layer 30 between the upper and lower substrates 10 and 20. In addition, a black-matrix layer 11 is formed on the upper substrate 10 to shield portions, except for pixel regions of the lower substrate 20, from the light, and a color filter layer 12 is formed to produce colored light within the pixel regions. Moreover, a common electrode 13 is formed on an entire surface of the upper substrate 10 including the black-matrix layer 11 and the color filter layer 12.
The lower substrate 20 is commonly called an array substrate, in which a plurality of thin film transistors, which serve as switching devices T, are disposed in a matrix configuration, and a plurality of gate and data lines 21 and 22 are formed to cross each other at the respective thin film transistors. In addition, the pixel region P includes a transmission part A and a reflective part R, wherein the transmission part A is an open area of a reflective electrode (not shown).
FIG. 2 is a cross sectional view of the transreflection-type LCD device of FIG. 1 according to the related art. In FIG. 2, the transreflection-type LCD device includes the upper substrate 10 having the common electrode 13 disposed thereon, and the lower substrate 20 having the pixel electrode 23. The pixel electrode 23 of the lower substrate 20 includes a transparent electrode 23a formed within portions corresponding to the transmission part A and the reflective part R, and on the reflective electrode 23b having the open area within the transmission part A. In addition, the liquid crystal layer 30 is formed between the upper and lower substrates 10 and 20, and a backlight 41 is provided below the lower substrate 20 to emit light during a transmission mode of the transflection-type LCD device.
When the transreflection-type LCD device is operated in a reflection mode, the ambient light or the front light is commonly used as the light source. Accordingly, the light B incident on the upper substrate 10 is reflected to the reflective electrode 23b, and then the light is transmitted to the liquid crystal layer 30 having liquid crystal molecules aligned by an electric field between the reflective electrode 23b and the common electrode 13. Thus, the light transmittance transmitting the liquid crystal layer 30 is controlled according to the alignment of the liquid crystal layer 30 to display an image.
During the transmission mode, the light F emitted from the backlight 41 provided below the lower substrate 20 is used as the light source. When the light F emitted from the backlight 41 is incident on the liquid crystal layer 30 through the transparent electrode 23a, the light transmittance is controlled by the alignment of the liquid crystal molecules in the liquid crystal layer 30. For example, the liquid crystal molecules are aligned by the electric field induced between the common electrode 13 and the transparent electrode 23a below a transmission hole to display an image.
FIG. 3 is an enlarged plan view of a pixel of a transreflection-type LCD device according to the related art. In FIG. 3, a unit pixel includes gate and data lines 21 and 22, a pixel electrode 23, and a thin film transistor T, wherein the gate and data lines 21 and 22 cross each other to define a pixel region. In addition, the pixel electrode 23 includes a transparent electrode 23a and a reflective electrode 23b within the pixel region, and the thin film transistor T is formed at the crossing point of the gate and data lines 21 and 22. The thin film transistor T includes a gate electrode 21a, a source electrode 22a, and a drain electrode 22b, and a scanning signal is supplied to the gate electrode 21a. In addition, the source electrode 22a protrudes from a portion of the data line 22 and receives video signals from the data line 22, and the drain electrode 22b is formed at a predetermined interval from the source electrode 22a to supply video signals to the pixel electrode 23. Then, a gate pad 31 and a source pad 32 are respectively formed at end portions of the gate line 21 and the data line 22 and are connected to drive ICs (not shown).
In FIG. 3, the pixel electrode 23 includes the transparent electrode 23a that is formed in portions corresponding to the transmission part A and the reflective part R, and on the reflective electrode 23b formed within the reflective part R, except for the transmission part A. Accordingly, the transparent electrode 23a is connected to the drain electrode 22b through a contact part C1 to receive the video signals. In addition, the reflective electrode 23b is formed to contact the transparent electrode 23a within the contact part C1 to which the video signals are supplied.
FIGS. 4A to 4H are cross sectional views along I-I′, II-II′, and III-III′ of FIG. 3 of an array substrate fabrication process of a transreflection-type LCD device according to the related art. In FIGS. 4A to 4H, the line I-I′ extends from a thin film transistor to a pixel region within a unit pixel region, the line II-II′ includes a section of a gate pad, and the line III-III′ includes a section of a source pad.
In FIG. 4A, a conductive metal layer is deposited on the transparent substrate 20, and is selectively removed using a first mask (not shown), thereby forming the plurality of gate lines 21 (in FIG. 3) and the gate electrodes 21a. Accordingly, as shown in FIG. 3, each gate line 21 includes a gate pad 31 at one end portion thereof, and the gate electrode 21a protrudes from the gate line 21. Subsequently, a first insulating layer 24, an amorphous silicon layer 25a, and an impurity layer (n+ layer) 25b are sequentially deposited on an entire surface of the transparent substrate 20.
In FIG. 4B, the impurity layer 25b and the amorphous silicon layer 25a are selectively removed using a second mask (not shown) to form an island-shaped semiconductor active layer 25 (later shown in FIG. 4C as semiconductor layer 35).
In FIG. 4C, a conductive metal layer is deposited on the transparent substrate 20 having the semiconductor layer 35, and is selectively removed using a third mask (not shown), thereby forming the plurality of data lines 22 (in FIG. 3) crossing the gate lines 21 (in FIG. 3), the source electrode 22a, and the drain electrode 22b. Accordingly, the source electrode 22a protrudes from each data line 22 (in FIG. 3) toward the semiconductor layer 35, and the drain electrode 22b is positioned at a predetermined interval from the source electrode 22a on the other side of the semiconductor layer 35. Subsequently, the impurity layer 25b of the semiconductor layer 35, which is exposed between the source and drain electrodes 22a and 22b, is removed using the source and drain electrodes 22a and 22b as a mask, thereby forming the semiconductor layer 35.
In FIG. 4D, an organic insulating layer is coated along an entire surface of the transparent substrate 20 including the data lines 22 (in FIG. 3), and exposure and developing processes are performed using a fourth mask (not shown) having a predetermined open area. Then, the organic insulating layer corresponding to the open area of the fourth mask is removed at a predetermined thickness. Then, a heat treatment is performed to form a first organic insulating layer 26a having embossing patterns at a portion of the organic insulating layer that is relatively thicker than the portion removed using the fourth mask. The organic insulating layer is formed of a positive-type organic insulating layer, such as Benzocyclobutene (BCB), or is formed of a positive-type material, such as photoacryl.
In FIG. 4E, a second organic insulating layer 26b having a constant thickness is coated on the first organic insulating layer 26a, wherein the second organic insulating layer 26b is formed of the same material as the first organic insulating layer 26a. Since the second organic insulating layer 26b is coated on the first organic insulating layer 26a at the constant thickness, it is possible to maintain the embossing patterns of the first organic insulating layer 26a after coating the second organic insulating layer 26b on the first organic insulating layer 26a. 
In FIG. 4F, the first and second organic insulating layers 26a and 26b are selectively removed using a fifth mask (not shown) having a predetermined open area, thereby defining the contact part C1 that exposes a predetermined portion of the drain electrode 22b and defining the transmission part A. After selectively removing the first and second organic insulating layers 26a and 26b, the remaining first and second organic insulating layers 26a and 26b are referred to as a first passivation layer 26. When selectively removing the first and second organic insulating layers 26a and 26b, the first and second organic insulating layers 26a and 26b corresponding to the gate and source pads are removed to expose the gate insulating layer 24 and the source pad 32.
In FIG. 4G, a reflective metal layer is deposited along an entire surface of the first passivation layer 26, and is selectively removed using a sixth mask (not shown), whereby the reflective electrode 23b is formed in the pixel region except for the transmission part A and the first contact part C1. Next, an inorganic insulating layer 27 of SiNx is deposited along the entire surface of the lower substrate 20 including the reflective electrode 23b. For example, the inorganic insulating layer 27 is deposited on the lower substrate 20 at a high temperature of 300° C. or more. However, the embossing patterns of the first passivation layer 26 are destroyed by thermal flow.
In FIG. 4H, the inorganic insulating layer 27 is selectively removed at the first contact part C1, the second contact part C2, and the third contact part C3 using a seventh mask (not shown), thereby forming a second passivation layer 27a. Subsequently, a transparent metal layer is deposited along the entire surface of the lower substrate 20 including the second passivation layer 27a, and is selectively removed using an eighth mask (not shown). Thus, the transparent electrode 23a is formed within the pixel region including the transmission part A and the first contact part C1. In addition, a gate pad terminal 33a is formed in the second contact part C2 to be connected with the gate pad 31, and a source pad terminal 43a is formed in the third contact part C3 to be connected with the source pad 32.
According to the related art, the embossing patterns (or concave pattern) are formed of the organic insulating layer to improve reflexibility of the reflective electrode by increasing a surface area of the reflective electrode having the embossing patterns.
FIG. 5 is a photomicrograph showing a peeling phenomenon of a reflective electrode according to the related art. In FIG. 5, after forming the organic insulating layer having the embossing patterns, the reflective electrode is formed. Then, the inorganic insulating layer, such as SiNx, is deposited at a temperature of about 300° C. Accordingly, the peeling phenomenon occurs due to stress caused by inferior adhesion between the reflective electrode and the organic insulating layer.
According to the related art transreflection-type LCD device, the embossing pattern (i.e., the concave pattern) is formed using a positive-type organic insulating layer, such as Benzocyclobutene (BCB), or using a positive-type photoacryl to improve the reflexibility. However, when using the positive-type organic insulating layer, mask process steps for forming the embossing pattern of the organic insulating layer must be performed, as well as the other mask process steps for removing the transmission part. Thus, according to the related art, a dual-coating process is required during the process for forming the organic insulating layer, thereby complicating fabrication process steps.
For example, when forming the embossing pattern using BCB, it is difficult to perform the complicated fabrication process steps, thereby degrading the reflexibility of the reflective electrode. In addition, since the positive-type photoacryl has a transition glass temperature, the thermal flow is generated at the high process temperatures, thereby destroying the embossing pattern of the first passivation layer due to the thermal flow.
Moreover, after forming the organic insulating layer having the embossing pattern (i.e., the concave pattern), the reflective electrode is formed on the organic insulating layer. Then, the inorganic insulating layer, such as SiNx, is deposited thereon, and the transparent electrode is formed. Thus, when the passivation layer of SiNx is deposited at the high process temperatures, it may generate the peeling phenomenon due to stress from the inferior adhesion between the reflective electrode and the organic insulating layer.